The prior art discloses different embodiments of such steering columns for adapting the position of the steering wheel to the seat position of the person driving a motor vehicle. In addition to height adjustment by virtue of the inclination of the steering column being set, it is possible, in steering columns of the type in question, for the steering wheel, which is fitted at the rear end of the steering spindle, to be positioned in the vehicle interior by virtue of adjustment in the longitudinal direction of the longitudinal axis of the steering column.
The length-adjustment capability is realized in that the actuating unit, consisting of an outer casing unit and of an inner casing tube, which encases the rotatably mounted steering spindle, can be pushed telescopically in and out and can be secured, i.e. fixed in a releasable manner, in different longitudinal positions by means of a releasable clamping device. The clamping device, also referred to as a securing device, acts on the outer casing unit, which is retained on the vehicle body, wherein in the open state of the clamping device—also referred to equivalently as the enabling or release position—it is possible for the inner casing tube to be displaced in the outer casing unit in order for the position of the steering wheel to be set and in the closed state—also referred to as the fixing position or securing position—the inner casing tube is braced in the outer casing unit and, during normal driving operation, the position of the steering wheel is fixed under the mechanical stressing which would be expected.
A known effective measure for improving occupant safety in the event of a vehicle collision, the so-called crash, in which the driver strikes against the steering wheel at high speed, is that of rendering the steering column so that, even in the fixing position of the clamping device, it can be longitudinally pushed together when the steering wheel is subjected to a high force which exceeds a limit value which arises only in the event of a crash. In order to ensure controlled braking of a body coming into contact with the steering wheel, an energy-absorption device is coupled in between the outer casing unit and the inner casing tube, which during normal operation are fixed to one another by the clamping device, but are pushed together relative to one another in the event of a crash. As a result, the kinetic energy introduced is converted into plastic deformation of an energy-absorption element, for example by virtue of a rip tab being ruptured or of an elongate bending element, for instance a bending wire or bending strip, being bent.
A steering column of the type in question is described in DE 10 2008 034 807 B3. The clamping device described in said document comprises an arresting element which is supported in the longitudinal direction on the outer casing unit and, when the clamping device is fixed in a direction transverse to the longitudinal direction, can be moved into force-fitting and form-fitting engagement with a corresponding engagement element on the inner casing tube in the fixing position. In the enabling position, the arresting element is lifted up from the engagement element, i.e. released, by the clamping device, and therefore the inner casing tube can be displaced in a longitudinal direction in the outer casing unit in order for the position of the steering wheel to be adjusted.
The engagement element is connected to the inner casing tube via an energy-absorption device which, during normal operation, is not subjected to stressing, i.e. forms a rigid connection between the outer casing unit and inner casing tube. In the event of a crash, however, the arresting element introduces such a large force into the engagement element that the outer casing unit and the inner casing tube move longitudinally in relation to one another, wherein the energy-absorption element is deformed and the movement is thus braked in a controlled manner.
Said document DE 10 2008 034 807 B3 also proposes rendering the braking action of the energy-absorption device controllable so that account can be taken, in the event of a crash, of whether the driver is strapped in or not or in order to be able to effect adaptation to parameters such as the driver's weight, distance from the steering and the like. In specific terms, for this purpose, at least two energy-absorption elements are provided, and these can be activated as required by virtue of a coupling means coupling them in between the outer casing unit and the inner casing tube, i.e. moving them into mechanical operative connection between the outer casing unit and the inner casing tube. For this purpose, it is possible, if required, to activate an actuator of the coupling means, for example a pyroelectric actuator or switch, also referred to as a pyroswitch, which mechanically couples the first or the second energy-absorption element, or both energy-absorption elements, into the flow of forces between the casing unit and the casing tube. This makes it possible to realize braking characteristics which are adapted to the respective requirement, in other words a so-called crash level.
The disadvantage with the previously known arrangement, however, is that the coupling means is fastened together with the energy-absorption elements on the inner casing tube and accordingly, during adjustment of the steering column, is moved along in the longitudinal direction, as a result of which a relatively large amount of movement or installation space is taken up.
A similar arrangement is described in US 2015/0375773 A1, in which a pyroelectric actuator of a coupling means is likewise fitted together with the energy-absorption elements on the inner casing tube. Although the energy-absorption elements are arranged in a space-saving manner on the one side of the casing tube, the amount of installation space required by the coupling means, which moves along during adjustment, is likewise disadvantageously large. The same applies, in principle, to the adjustable steering column which is known from DE 10 2009 009 577 B3.
Thus a need exists for a steering column that has at least two crash levels and consumes less installation space.